The England and City winger acknowledges United's years of dominance but believes it 'could all change' in the next 12 months.
City lifted the FA Cup and also qualified for the Champions League for the first time last season and are expected to embark on another spending spree this summer.
Sea change: Winger Adam Johnson predicts that Manchester City could overtake United as the leading club
Johnson said: 'United have been on top for decades now. But I think we are definitely closer.'I think we are probably as close as we ever were. I think everyone knows that now.
'Maybe if you tweak the squad a little bit, we could give it a massive push next season, and who knows, it could all change.'
But Johnson believes it is vital City keep hold of leading scorer Carlos Tevez. Tevez once again has a question mark hanging over his future despite City boss Roberto Mancini declaring he was optimistic the striker would remain at Eastlands.
Johnson, currently preparing for England's Euro 2012 qualifier with Switzerland on Saturday, said: 'Carlos carries us sometimes with his goals and his drive. Personally he is probably the best player I have played with.
Up for the cup: Johnson lifts the trophy after City's victory over Stoke City in the FA Cup final at Wembley in May
'Some of the goals, and some of the stuff he does in training, is just unbelievable. Personally I hope we keep hold of him just like all the City fans do.
'He will be a major part next season when we are playing in the Champions League. He would be hard to replace. There are probably only five or six strikers out there who get you that many goals a season at the highest level. We have one of them, so it would be great if we could keep him.'
Johnson believes playing in the Champions League will only enhance his prospects of becoming a regular player with England.
He said: 'Personally it's going to help me playing week in week out in the Champions League, and doing well, and I will have a chance to be in most of the (England) squads.
'Watching this season's final certainly whets your appetite to be involved in such things.
'That's what you are in football for, Champions League finals, with the best players and the best teams in the world. We are going to get the chance to do that next season.'
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Source: Daily Mail
Source: Daily Mail